[ltt-dev] [RFC] New UST 2.0 Tracepoint Event API

[Nathan Scott]

Hi Mathieu,

On 28 July 2011 05:06, Mathieu Desnoyers <mathieu.desnoyers at efficios.com>wrote:

> Hi all,
>
> I'd like to get feedback on the new UST 2.0 tracepoint event API.
> The code still needs to be debugged (it does not compile yet), but the
> basic structure of the API is in place, and I'd like to get feedback on
> this.
> ...
> Note: the print formatting information is actually metadata exported for
> the trace viewer. It does not add information to each event in the
> trace.

...

The tracepoint.h header contains a lengthy comment describing the
> TRACEPOINT_EVENT() API, along with a usage example:
>
> http://git.lttng.org/?p=ust.git;a=blob;f=include/ust/tracepoint.h
>
> The macros describing the types available within the TP_FIELDS macro are
> described at the beginning of:
>
>
> http://git.lttng.org/?p=ust.git;a=blob;f=include/ust/lttng-tracepoint-event.h
>
>
This link appears to be broken...?  The examples in the email didn't seem
to
mention floating point trace info - is that catered for?  Its not so useful
in the
kernel, but for userspace tracing its much more likely to be needed I guess.

Thoughts ?
>

In addition to the type information that the format string provides, it
could also
be very useful for a consumer tool to be able to tell the units of the trace
data -
bytes, kilobytes, milliseconds, nanoseconds, etc.  Not sure I can think of a
neat
way to add that into the API though - perhaps extending the format string
with
optional type decorator?  Might be a bit counter-intuitive/ugly.

Other random thoughts that occur - I've seen some tracing systems that have
a
"trace caliper" concept, where the start (say, of a transaction) and the end
can
be linked ... would this be useful as an explicit part of the API, or is it
something
that could/should be built at a higher level?  These other tracers also tend
to do
what they call "end-to-end" tracing, where a trace hierarchy can be built
(using the
caliper start/end concepts) - not sure how that would be added to the API,
but just
thought I'd throw it out there for your consideration anyway.

HTH.

cheers.

--
Nathan
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